Conventionally, natural fibers (such as cotton) and the general organic fibers have been used as an incision-resistant material. Gloves made by knitting up those fibers etc. have been often used in the field which needs incision-resistant.
Then, knits, textiles, etc. which consist of spun filament of high strength filaments, such as an aramid fiber, for providing the incision-resistant function have been devised. However, there was dissatisfaction in the viewpoint of a hair omission or durability. Although trials which improve incision-resistance by on the other hand using metal fibers together with organic fibers or natural fibers as another means are performed, the drape of textures becomes hard by using metal fibers, and there is thus a problem that pliability is impaired.
For example, the fiber reinforced concrete which is made by kneading metal fibers, glass fibers, carbon fibers, polyvinyl alcohol fibers, or various olefin fibers to various cement mortar or concrete materials is developed as a method of improving the brittleness which is a defect in the structure material of cement mortar and concrete (for example, JP-B-58-18343, Japanese patent No. 2,510,671). However, although the reinforcing effect by adhesion with a concrete matrix is excellent, the fibers for these reinforcement, such as metal fibers represented by steel fibers, essentially have large specific gravity which results in a defect that a structure made thereof becomes heavy, and in addition, the strength of the structure is degraded due to generation of rust. Therefore, the fibers are unsuitable as structure material for such as harbor facilities or skyscrapers asked for a weight saving.
On the other hand, for inorganic fibers, glass fibers have an inferior in alkali resistance and carbon fibers have a problem in that the fibers become bended or cut during kneading. In addition, polyvinyl alcohol fibers or polyolefin fibers, especially polypropylene fibers which are organic fibers, are low in tenacity, and thus have a problem of reduction in slump due to a need to increase the incorporation of the fibers to a large extent for achieve a sufficient effect. Although polyethylene fibers with ultra-high molecular weight are excellent in strength or alkali resistance, the fibers have a problem in that stiffness of the fibers is low and they easily get twined with each other to become a lump during kneading due to the flatness of the cross section.
Conventionally, twists of synthetic filaments, such as vinylon, polyester filament, and nylon, have mainly been used for a rope. In recent years, although a monofilament of fluorocarbon or nylon, as well as the interlace of a nylon monofilament came to be used for the rope, the rope of the interlace structure of a nylon monofilament had an inadequate tensile strength and thus was sometimes broken in the ocean area especially with wild waves. In addition, an improvement was desired also in respect of wear resistance and durability. Further, since the tensile strength was not high enough, the rope itself should be thick inevitably and the nature for containment and handling were remarkably bad.
As a polyethylene filament with a high strength, there is known a filament which is produced from an ultra-high molecular weight polyethylene by a so-called “gel-spinning method and melt spinning” and which has such a high strength and such a high elastic modulus that any of conventional filaments has never possessed, as disclosed in JP-B-60-47922 and JP-A-62-257414 for example, and this filament has already come into industrially wide use.
A high strength polyolefin filament produced by melt spinning is disclosed in, for example, U.S. Pat. No. 4,228,118. According to this patent, the process for producing a high strength polyethylene filament disclosed comprises extruding a polyethylene having a number-average molecular weight of at least 20,000 and a weight-average molecular weight of less than 125,000 through a spinneret which is maintained at the temperature between 220 and 335° C., then taking over the polymer at the rate of at least 30 m/min. followed by drawing it at least 20 times at the temperature between 115 and 132° C. Thus the filament has a tenacity of at least 10.6 cN/dTex.
Moreover, JP-A-08-504891 discloses a high strength polyethylene filament which is produced by melt spinning polyethylene with high density through a spinneret, and then drawing the obtained fiber at the temperature of 50-150° C. The process for production is characterized in that the polyethylene provided for melt spinning is a homopolymer of ethylene which satisfies the conditions of having a weight-average molecular weight (Mw) of 125,000 to 175,000, a number-average molecular weight (Mn) of 26,000 to 33,000 and a polymer dispersibility (Mw/Mn) of less than five, as well as a density of larger than 0.955 g/cm3, and that the extent of draw ratio at the draw stage is at least 400%. This patent is characterized by controlling the polymer dispersibility and the density of polyethylene as a starting material to the above-mentioned value.
In addition, JP-A-11-269717 discloses a high strength polypropylene filament made from a crystalline polypropylene with a weight-average molecular weight of 200,000 to 450,000, although the tenacity of the high strength polypropylene filament obtained according to the patent is at most about 13 cN/dtex. This patent is characterized by blending two kinds of polypropylene as starting materials each of which has a different melt flow rate, performing melt spinning, and drawing said filament to 5 times or more under the draw temperature of 120-180° C., using a pressurized steam.
Production cost becomes very high from the industrial viewpoint since a mixture of a solvent and a polymer is used in gel-spinning and solution-spinning. That is, by the method currently disclosed in this patent, the concentration of polyethylene as a starting material is at most 50% or less, and thus is lacking in productivity. If a solvent is used, incidental facilities, such as an equipment for recovery/purification and the like, will certainly be needed, which is thus expensive. Additionally, it is not desirable in respect of environment.
Furthermore, with respect to a melt spinning, although some arts are known, a high strength of said filament is attained only by the very limited conditions for production.